PROJECT SUMMARY Approximately 11,000 spinal cord injuries (SCI) occur annually, with 80 % of injuries occurring in men. Onset of SCI typically reduces participation in physical activity and alters endocrine function, body composition, and vitality, leading to reduced health status. Another serious complication of SCI is osteoporosis. Bone loss is rapid in the initial six months post-injury and is greatest in sites such as the tibia and femur that typically receive skeletal loading. This demineralization enhances occurrence of fracture in everyday activities involving little to no trauma. Because bone loss and subsequent fractures lead to severe clinical, psychological, and financial complications, early intervention to slow rate of bone loss in persons with SCI is essential. To slow progression of osteoporosis in this population, various rehabilitation modalities have been used, although their ability to maintain or even increase bone in this population is equivocal. One study reported that single mode exercise by itself is unable to slow bone loss in individuals with SCI. To date, no study has examined the effects of rehabilitation consisting of multiple exercise modalities providing loading of the lower extremities on bone health and body composition in this population. Moreover, no study has measured alterations in bone status, using bone biomarkers, in response to long-term exercise training. Consequently, the primary aim of this study is to examine changes in bone mineral density (BMD), bone health, body composition, and quality of life in response to a rigorous, multi-modal training program characterized by bone loading. Overall, bone loss is a significant complication of SCI presenting tremendous challenges to the clinician. Practical and effective methods must be identified to manage and mitigate bone loss, and improve overall health status, in this population. We propose a novel six-month training study in approximately 24 men and women with SCI. They will complete 6 - 9 hours per week of intense multi-modal rehabilitation focusing on lower extremity loading. Their responses will be compared to five adults with SCI who do not complete this mode of exercise. Bone mineral density (BMD), a clinically valid index of bone strength and fracture risk, will be assessed at four sites (spine, total body, hip, and knee) at baseline and at three and six months of the program. Body composition consisting of fat and fat-free mass will be assessed. Blood samples will be obtained at similar intervals to assess alterations in bone growth and resorption during training. Quality of life will be assessed to examine alterations in health outcomes in response to training.